Such angular adjustment systems known as VCT (variable cam timing) systems, are often used in internal combustion engines to displace the position of the camshaft in relation to the crankshaft. The phase shift of the valve opening and closing times that is possible by the angular adjustment enables the valve timing to be optimised with respect to the nominal output, torque, fuel consumption and exhaust gas emission requirements of the engine.
The angular adjustment is mostly performed hydraulically by means of an internal adjusting device fitted in the camshaft driving unit. For this purpose a helical gear is fitted between the chain wheel and the camshaft, and a hydraulic piston effects an axial displacement of the helically toothed element such that an angular displacement results between the driving gear and the camshaft. The form of the adjusting device can be such that advancing or retarding of the valve timing is brought about through two alternately pressurised hydraulic ducts. The valve elements required for the control are suitably located in the non-rotating part of the system. Alternatively the control can be effected through only a single hydraulic duct through which the angular adjustment in one direction takes place, while the angular adjustment in the other direction is effected by means of a return spring.
A characteristic feature of the hydraulic adjusting devices usually used is that they are connected to the rotating camshaft. The hydraulic fluid must be supplied to the rotating adjusting device from a non-rotating hydraulic supply. For this purpose in the known systems a non-rotating end cap is provided which has a recess in it for a rotating oil distribution device. Both in the end cap and in the rotating oil distribution device at least one oil distribution duct is provided which, in the transition region between the non-rotating and the rotating elements, changes into at least one annular duct. Elastic sealing elements are provided for sealing of the annular ducts between the end cap and the rotating oil distribution device. Since the end cap is connected to the camshaft so as to rotate therewith, it is centred on the camshaft. At the same time the end cap forms a portion of the outer side wall of the engine block. The outer side wall is connected at its upper face to the cylinder head cover of the engine, and the upper edge of the outer wall must be in alignment with the cylinder head cover in order to ensure the oil-tightness of the outer wall of the engine block.
The position of the cylinder head cover relative to the axis of the camshaft is subject to quite large manufacturing tolerances arising in mass production. These tolerances affect the position of the outer side wall fitted to the cylinder head cover. For this reason in the prior art the outer side wall is made up of two parts, one being the end cap and the other the side housing. The side housing has a recess to receive the end cap, the rim of the end cap being secured on the outside of the side housing, for example by means of a screw connection, in such a way that deviations in the relative position of the side housing and the end cap can be compensated during assembly. Between the side housing and the end cap an elastic sealing element is provided in order to prevent loss of oil.
However, during the lifetime of the engine each sealing element needed on the outer housing of the engine block can become leaky, and consequently represents a possible source of problems which give rise to maintenance and repair costs. In addition the length of the engine block is increased through the end cap projecting beyond the external profile of the side housing, which could be avoided by a one-piece design of the side wall.
Object of the Invention
An object of the invention is to provide an angular adjustment device of the aforementioned kind which is as easy as possible to fit and in which the outer side wall is formed in one piece with the end cap while at the same time ensuring the necessary adjustment for tolerances between the position of the side wall and the camshaft axis.
The Invention
To this end, in accordance with the invention the end cap has, in its inner circumferential region facing the direction of adjustment, at least one recess shaped to receive an oil distribution ring, the oil distribution ring is shaped so as to be connectable non-rotatably to the end cap and is arranged to be movable transverse to the common axial direction, the internal diameter of the recess is greater than the external diameter of the oil distribution ring, and the oil distribution ring has radially extending passages distributed around its circumference.
Fitting the non-rotatable oil distribution ring inside the non-rotatable end cap so as to be movable transverse to the common axial direction makes it possible to achieve the necessary compensation of tolerances by a movement of the oil distribution ring relative to the end cap. Consequently in accordance with the invention the end cap can be formed so that at the same time it forms the side housing of the engine block which at its upper end face is in alignment with the cylinder block head.
Between the outer circumference of the oil distribution ring and the inner circumference of the end cap an annular gap is formed, the diameter of which is adapted to the maximum tolerances that have to be compensated for. If the oil distribution ring is moved, the end cap and the oil distribution ring are in general no longer lined up concentrically with one another, so that the annular gap is then narrower at one side and wider at the other.
The supply of the hydraulic oil to the angular adjustment device takes place through ducts formed within the end cap first of all into the annular gap between the end cap and the outer circumference of the oil distribution ring. From here the oil passes through the radially extending passages provided in the oil distribution ring into the annular gap between the oil distribution ring and the rotating oil distribution device. In the oil distributing device the oil is supplied through ducts in the angular adjustment device.
If two hydraulic ducts are used for control of the angular adjustment device, it is provided in accordance with the invention that the end cap has in its inner circumferential region, facing the direction of adjustment, two recesses having different diameters and forming a step and the oil distribution ring has a similarly stepped form at its outer circumference, the internal diameters of the recesses being greater than the associated external diameters of the stepped oil distribution ring, so that two annular ducts are formed which are separated from one another. The stepped form of the inner circumference of the end cap and the outer circumference of the oil distribution ring enables two annular ducts, separated from one another, to be formed, the separation being effected by the mutually contacting flanks of the steps on the end cap and on the oil distribution ring. The separation of the ducts is necessary since leaks between the ducts impair the functioning of the angular adjustment. Separate ducts for the hydraulic oil are similarly provided in the end cap, the oil distribution ring and the oil distribution element.
In a further embodiment of the invention an annular sealing element is provided between the flanks of the stepped oil distribution ring and the flanks of the stepped end cap. This sealing element gives additional sealing of the two ducts from one another.
According to another embodiment of the invention the end cap can have on its side facing the camshaft a radially inwardly extending retaining device for the oil distribution ring. After the oil distribution ring has been fitted the retaining device is attached by means of a snap fastening on the side of the end cap facing the camshaft. A screw can be provided for additional security. The retaining device serves firstly to fix the oil distribution ring in its axial position and secondly to close the side of the annular gap between the end cap and the oil distribution ring.
According to yet another embodiment of the invention a retaining pin is provided to prevent any rotary movement of the oil distribution ring. The retaining pin is either located on a non-rotating part of the housing and engages in a recess in the oil distribution ring, or the retaining pin is provided on the oil distribution ring and engages in a recess in the end cap. The recess is of such a size that the movement provided in accordance with the invention transverse to the common axial direction between the end cap and the oil distribution ring to produce the required tolerance compensation is possible.